As shown in FIG. 5, conventionally, a cryogenic tank for storing the above-described low-temperature liquefaction fluid comprises a dual construction including an inner tank 3, an outer tank 6 and an insulation 14 interposed therebetween. Further, the lateral side of the outer tank 6 comprises an integrated assembly of an outer shell 13 having air-tightness for preventing intrusion of moisture component from the outside, and a dike 4 for preventing spreading or diffusion of low-temperature liquefaction fluid L to the outside when the liquid L accidentally leaks from the inner tank 3.
According to a construction conventionally employed as such dual construction cryogenic tank, its inner tank 3 is constructed as a metal tank, and its outer tank 6 is comprised of the outer shell 13 of a metal lining construction and the dike 4 formed of concrete material.
More particularly, the inner tank 3 is constructed as a steel vessel made of e.g. 9% nickel steel (9% Ni steel) having high toughness at ultralow temperatures in order to store therein the low-temperature liquefaction fluid L (about −160° C. in the case of LNG) (see Patent Document 1). The dike 4 portion of the outer tank 6 is formed of e.g. concrete material so as to temporarily preventing leakage of the low-temperature liquefaction fluid L when or if this fluid L should leak from the inner tank 3. As this concrete material, there is employed pre-stressed concrete (PC) provided with enhanced strength by applying compression force to concrete material. Further, on the inner face of the concrete dike constituting the outer tank 6, there is provided a cold resistant relief formed of glass mesh, polyurethane foam or the like. Namely, when the low-temperature liquefaction fluid L comes into direct contact with the inner face of the concrete of the outer tank 6, this may cause crack in association with sudden change in the temperature of the concrete face due to the direct contact, which crack would prevent the dike from providing its intended function. The above layer is provided for preventing such inconvenience (see Patent Document 2).
[Patent Document 1] Japanese Patent Application “Kokai” No. Hei. 10-101191
[Patent Document 2] Japanese Patent Application “Kokai” No. 2002-284288